Mortgage Loans TDRs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) contracts	Dec. 31, 2017 USD ($) contracts	Dec. 31, 2016 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	109 months	153 months	157 months
Average interest rate reduction of a single-family modified loan	0.21%	0.56%	0.79%
Number of loans troubled debt restructurings activity | contracts	95,826	66,414	69,811
Recorded investment troubled debt restructurings activity | $	$ 14,427	$ 9,342	$ 9,681
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	95,812	66,406	69,800
Recorded investment troubled debt restructurings activity | $	$ 14,353	$ 9,243	$ 9,615
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	89,192	59,708	61,586
Recorded investment troubled debt restructurings activity | $	$ 13,437	$ 8,247	$ 8,405
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	115	171	186
Recorded investment troubled debt restructurings activity | $	$ 11	$ 18	$ 20
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	5,378	5,369	6,647
Recorded investment troubled debt restructurings activity | $	$ 697	$ 771	$ 946
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	1,127	1,158	1,381
Recorded investment troubled debt restructurings activity | $	$ 208	$ 207	$ 244
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	14	8	11
Recorded investment troubled debt restructurings activity | $	$ 74	$ 99	$ 66